Police have issued a warning about a surge in a new type of crime which has followed a surge in thefts from cars across the country.

There have also been 15 thefts from cars in one Merton ward in less than three months, with two in which there was no sign of forced entry.

The new crime method is nicknamed "jamming"
in which thieves have worked out a way to interfere with the car's central locking systems, enabling them to block the "plipper" signal from the remote that opens and locks doors.

Many central locking systems now are operated by a plipper that connects the car on a radio frequency. The signal locks or unlocks the doors and in some cases, activates the alarm. The weakness exploited by thieves is that other devices using similar radio frequencies can be bought in the high street or on the internet.

Thieves will activate the device at the same time a car owner attempts to lock their vehicle and then "jams" the radio frequency. Owners may think their vehicle is locked and leave their vehicle unattended, giving thieves the chance to gain access to the vehicle.

Police are warning drivers to make sure they listen for the tell-tale clunk or wait for the indicators to flash, to ensure that the car is locked.

Police in the Raynes Park ward said there had been
15 thefts from motor vehicles from October 19, 2010 to January 11, 2011. The thieves have accessed the cars by a variety of means, from smashing windows, to piercing/drilling locks. In two of the thefts there was no sign of forced entry.